The present invention relates to a method for receiving signals in the for of carrier oscillations modulated by a useful signal, in which the type of modulation used for an incoming signal is first determined with a histogram and from this, control information is produced for adapting a circuit recovering the original signal to the type of modulation determined.
A radio receiving device or Morse Code signals or teletype signals, which makes use of such a method and in which the incoming signal is first supplied to a computing circuit which generates from it a histogram of signal frequencies plotted against time, is disclosed, for example, in German reference No. DE 3 414 969 C2. This generated histogram is then compared with model histograms stored in a memory and via this comparison the type of modulation of the received signal is determined. Following the determination of the type of modulation, the discriminator is adapted to this type of modulation and the received signal is fed to the discriminator.
As has been found, such a method is of significance not only in receiving devices for radio signal monitoring, but also in networks for information and data transmission if in such a network groups of transmitting/receiving devices exist which exhibit different types of modems. In that case, only transmitting/receiving devices exhibiting the same type of modem can ever communicate with one another. Such networks are mandatorily produced in the international co-operation of institutions, the transmitting/receiving devices of which meet different CCITT recommendations with respect to the type of modulation used.
If a subscriber with priority in such a network has the requirement to be able to communicate with any of the remaining subscribers of the network if necessary, a universal transmitting/receiving device is needed which, with respect to its modem, can be adapted to the type of modem of the distant station.
Basically, of course, the possibility exists to equip such a universal transmitting/receiving device with several types of modems and, before the signal transmission, to activate the type of modem used at the distant station in the local receiver, for example by means of a consultation. Apart from the fact that such a universal transmitting/receiving device necessitates a relatively large technical expenditure which has great disadvantages especially for mobile use (increased weight, increased volume, increased power requirement), it must also be possible to set up a connection quickly if the type of modem of the transmitting station is not known to the universal transmitting/receiving device.